The proposed conference will be the sixth in a series of Gordon Conferences on the heart which began in 1966 under the auspices of the Cardiac Muscle Society. The activation process in cardiac and skeletal muscle has been the subject of much experimentation within the last few years, and this conference will be particularly timely in delineating the problems which still remain unsolved in this field. It will bring together a variety of different approaches: electrophysiological studies, which have elucidated the mechanism of impulse spread within the depths of muscle fibers and have provided new information about the physiological mechanism of calcium release; electron microscopic studies, which have helped to characterize the structural basis for the intracellular regulation of calcium stores; and mechanical studies, both in intact fibers and skinned fibers, which have recently changed our ideas about the development of contractile activity and its relation to the entry of calcium into the myoplasm. Within the framework of the proposed conference, there will be a great deal of interchange between investigators in the cardiac and skeletal areas (smooth muscle will be covered in the 1973 Conference). There will also be ample opportunity for discussion between investigators of basic jenomena and workers who are more clinically oriented. Topics of particular clinical relevance include the mode of action of catecholamines on the cardiac action potential and of various inotropic agents on myocardial contractility, as well as the cellular basis for the Bowditch staircase. Several of the proposed conference sessions focus on very recent advances in muscle research which have not been previously discussed in similar meetings. For this reason, it should be particularly advantageous to have a conference in a setting which favors free and informal exchange of ideas between a wide range of scientists whose common interest is activation in muscle.